This invention relates to the electrical installation of control devices. More particularly, this invention relates to interface circuitry for facilitating the installation of a control device in a commercial, industrial, or home electrical environment.
Such electrical environments are typically powered by an alternating current (AC) power source which, by convention, delivers current through a utility hot and a utility return. The current alternates between positive and negative values typically 60 times a second (i.e., 60 hertz). If either the hot or return is electrically disconnected, current will not flow. By convention, the hot conductor is used to switch an electrical load, such as room lighting, on and off, while the utility return is maintained intact. The utility return is made up of two redundant conductors called neutral and equipment ground. These two conductors are by convention electrically coupled at the power source or at the main circuit breaker panel. Throughout the wiring of an AC system, both the hot and utility return conductors are physically adjacent each other for safety reasons.
A third utility path known as an isolated earth ground is sometimes provided. This third path is an isolated conductor between the electrical point of use (e.g., an electrical outlet) and the physical earth ground. The isolated earth ground conductor is not electrically connected to either the utility hot or utility return.
When installing a control device (for example, an occupancy detector) in place of a traditional toggle switch, by convention three conductors are accessible--a hot, a load, and a utility return--requiring three separate connections to be made. In many cases, it is not possible to safely determine the hot from the load. For example, the conductors may not be color coded, or they may be coded incorrectly or contrary to local custom. The possibility of an incorrect installation is thus undesirably high.
To check for an incorrect installation, the device should be tested after it is installed. However, testing can be very time consuming; many control devices, such as the previously mentioned occupancy detector, have built-in time delays. Furthermore, testing at the time of installation may not always be possible, because, for example, the power may be off or particular testing equipment may not be available. It is therefore likely that either the device will not be tested at all or installation costs will be higher. Moreover, if the device fails to function, it could be assumed to be defective when it may only be incorrectly wired, thus resulting in a perfectly good device being wasted. To prevent such waste, the device should therefore be removed, rewired, and retested. However, this activity further increases installation time and costs.
In addition, many known control devices do not advantageously limit the amount of current supplied by the power source during periods of low current demand. For example, current demand in an occupancy detector is at a minimum when the detector monitors an unoccupied area (i.e., the load is off and the detector is essentially in a stand-by mode). Any resulting current undesirably increases power consumption and accordingly the electrical costs of operating the device. Such costs can become significant in applications where hundreds of control devices are deployed, such as, for example, in large industrial complexes. Limiting the current supplied during low demand periods reduces power consumption and results in more economical operation of the device.
In view of the foregoing, it would be desirable to provide interface circuitry that facilitates the installation of a control device by eliminating the need to determine which conductor is the load and which is the hot.
It would also be desirable to provide interface circuitry that reduces the cost of operating a control device by selectively limiting the amount of current supplied to the device by the power source.
It would further be desirable to provide interface circuitry that reduces the number of conductors that must be coupled during installation of a control device.